Case Study
The Badger Army Ammunition Plant (BAAP) located in the Baraboo Hills of central Wisconsin once produced propellants for cannons, rockets, and small arms rockets. Production began in 1942 for use in WWII, and continued until 1975 shortly after the end of the Vietnam War. Today the workers are gone, but they left behind a legacy of contamination. Contaminated soil covers about 2 percent of the 7,354 acre facility and a plume of contaminated groundwater has migrated off site to the south.
Instead of dealing with the contamination as one large area the facility has been divided into 8 primary areas. This case study looks at the Settling Ponds area located along the southern boundary of the facility. During production a series of four settling ponds received wastewater and surface water runoff. Water reaching the final pond was discharged to Lake Wisconsin on the Wisconsin River. In the 1970's as part of remedial activities a portion of the soil in the settling ponds was excavated and placed in five spoils disposal areas. Together the ponds and spoils disposal areas consist of about 88 acres.
Initial soil cleanup objectives for the Settling Ponds area were established in 1994. For the most part these cleanup objectives were based upon laboratory detection limits or background concentrations. Establishing cleanup criteria based on detection limits was standard practice at the time. However, it offers little insight related to potential threat to the environment posed by the contamination. In addition, advances in laboratory technologies were pushing contaminant detection limits lower. In many cases the detection limits were lowering from the parts per million, to the parts per billion, and in some cases even to the parts per trillion range. It became obvious to everyone that cleaning up to such extremely low concentrations at the BAAP and other locations would be quite costly.
To solve the problem regulatory agencies developed risk-based cleanup objectives guided by toxicological studies. For example soil standards were now based on the estimated mass of contaminated soil being ingested and the health affects of doing so. This is simple enough a process when dealing with direct contact exposure to contamination. Unfortunately, contaminants typically don’t stay where they were put. They can volatilize to the atmosphere or leach to groundwater and these exposure routes must be considered when developing risk-based cleanup objectives. One approach is to implement long-term monitoring to see if the contaminants reach a receptor. The problem with this approach is that if the contamination reaches the receptor, the intervening soil or groundwater has become contaminated. Furthermore, simple monitoring cannot determine if a particular area of contamination is still acting as a source.
Why Wait?
Instead of waiting for the contaminants, computer modeling can predict years of contaminant migration in minutes. Knowing this, regulatory agencies have used computer models like SESOIL and AT123D to establish baseline cleanup objectives. To ensure environmental protection these baseline standards are typically based on the worst case scenario. As most contamination was not released in the worst case scenario, regulatory agencies allow for the development of site-specific cleanup concentrations. For the most part this consists of using the same models but with site specific input parameters.
Scope of Work
To provide for improved environmental protection, site-specific cleanup objectives were established for contaminated soil located in the settling ponds and spoils disposal areas. As part of this process the list of contaminants were reevaluated based on current toxicological information. Soil impacts were evaluated for protection from direct contact exposure and protection of groundwater quality. Protection of human health and the environment from direct contact was evaluated using statistical methods. Transport and fate modeling was performed to evaluate risk to groundwater quality.
Modeling was performed using the SESOIL and AT123D models in the SEVIEW package. SEVIEW was selected for several reasons including: easy of use, and because SESOIL was used by the Wisconsin Department of Natural Resources (WDNR) to develop baseline cleanup objectives for soil. In fact SEVIEW was designed based on the baseline modeling performed for the WDNR. The SESOIL Pollutant Cycle reports were used to assess contaminant fate in soil under site conditions. SESOIL calibration was assessed using the Hydrologic Cycle report. Finally the AT123D Point of Compliance (POC) reports were used to establish predicted groundwater concentrations and the resulting site-specific cleanup concentrations.
These reports are unique to SEVIEW. Other programs primarily focus on setting up the models. For the most part users are left to find their own way of examining the extremely large output files to determine what the models predicted. Using this approach it often takes longer to figure what was predicted than it took to run the models.
Land Use
Land use is an important part of the risk-based process. This is because exposure guidelines differ for residential and industrial settings. Although not finalized current plans are for the BAAP to be divided in to three parts.
The largest portion (3,850 acres) will be added to Devils Lake State Park which borders the BAAP to the north. Devils Lake State Park is Wisconsin’s most popular park receiving approximately 1.4 million visitors per year. The next largest portion (1,950 acres) will be used by the US Dairy Forage Research Center (USDRFC). The USDFRC is a part of the US Department of Agriculture and is associated with the University of Wisconsin-Madison. The remaining 1,500 acres will be given to the Ho-Chunk Nation. Plans are for the land to be primarily used for prairie restoration and bison habitat.
Given these potential land use options it was determined that the most restrictive residential exposure option should be used.
Results
Based on both direct contact exposure and protection of groundwater quality the degree and extent of contaminated soil was significantly reduced. Application of these site-specific cleanup concentrations could provide up to a $30 million cost savings. Furthermore, use of these site-specific values will also provide for improved protection of human health and the environment. The modeling portion of the work was completed quickly and the SEVIEW reports assisted in report preparation making the job much easier.
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